Calculating Weeks (2000/XP)

I have a time card table that the user would like to have a report run on. The report has to sum the data for each possible week. i.e. each record has a date in it. Assuming a week starts on Sunday and finishes on Saturday, I want to total the data for each week, regardless of start and end dates of the data in the table. The only way I can think of is to have an arbitrary start date (a Sunday) and calculate each subsequent Saturday and then somehow assign the appropriate week # or ending date to each record for totalling purposes. Any other ideas out there?